I'm planning on making a 6m vertical dipole, using a tube lower element
(shield side) to run the coax to the center point.
I have an almost perfectly sized stainless steel whip (old CB antenna), and
already have a slightly longer section of copper pipe to use for the bottom
that I can easily cut down. A friend that makes custom plastic stuff says if
he has the proper sized scrap he'll bore and cut a plastic insulator/whip
support for me... if not he'll get the stuff at cost.

Mounted sideways it would look something like this:
- Steel Whip
+ Feedpoint/section insulator/whip support
= Copper pipe with feedline (coax) running through it to feed point
------------------------+===============
Left side connected to center conductor at feedpoint
Right side connected to shield at feedpoint

What I'd like to know is if it is going to have a major effect on my
dimensions/bandwidth/anything else if I use different materials for the two
sections of the dipole (steel for the whip, copper for the pipe)? And what
kind of effect is having the two different element sizes going to have as
well? (I know increasing element sizes tends to raise overall bandwidth, but
not sure how only one element will effect the antenna as a whole.)

Also is there going to be any effect from the capacitance between the shield
braid of my coax and the antenna segment surrounding it? The website I read
this from didn't mention that, though they did say you may want to coil the
feedline about 4-6 turns about another quarter wavelength from the end of
the antenna.

Thanks in advance
73
KD4COX, Eric
--

On Fri, 9 Apr 2004 14:13:07 -0500, "Tyas_MT"
wrote:

I'm planning on making a 6m vertical dipole, using a tube lower element
(shield side) to run the coax to the center point.
I have an almost perfectly sized stainless steel whip (old CB antenna), and
already have a slightly longer section of copper pipe to use for the bottom
that I can easily cut down. A friend that makes custom plastic stuff says if
he has the proper sized scrap he'll bore and cut a plastic insulator/whip
support for me... if not he'll get the stuff at cost.

Mounted sideways it would look something like this:
- Steel Whip
+ Feedpoint/section insulator/whip support
= Copper pipe with feedline (coax) running through it to feed point
------------------------+===============
Left side connected to center conductor at feedpoint
Right side connected to shield at feedpoint

What I'd like to know is if it is going to have a major effect on my
dimensions/bandwidth/anything else if I use different materials for the two
sections of the dipole (steel for the whip, copper for the pipe)? And what
kind of effect is having the two different element sizes going to have as
well? (I know increasing element sizes tends to raise overall bandwidth, but
not sure how only one element will effect the antenna as a whole.)

Also is there going to be any effect from the capacitance between the shield
braid of my coax and the antenna segment surrounding it? The website I read
this from didn't mention that, though they did say you may want to coil the
feedline about 4-6 turns about another quarter wavelength from the end of
the antenna.

Thanks in advance
73
KD4COX, Eric

Eric,
You've essentially described a 'sleeve dipole', dont sweat it about
interaction between the copper pipe and the coax inside - though you
may wish to secure the lower end as well so it doesn't rattle around
inside the pipe. As to the use of different materials affecting
performance, shouldn't be an issue. Make sure though that you cut the
elements on the long side so you can trim to optimum length. You may
wish to do a Google search on 'sleeve dipole' and see if you find any
info that will help.

Good luck,
Howard
KE6something or other

"Tyas_MT" wrote in message
...
I'm planning on making a 6m vertical dipole, using a tube lower element
(shield side) to run the coax to the center point.
I have an almost perfectly sized stainless steel whip (old CB antenna),
and
already have a slightly longer section of copper pipe to use for the
bottom
that I can easily cut down. A friend that makes custom plastic stuff says
if
he has the proper sized scrap he'll bore and cut a plastic insulator/whip
support for me... if not he'll get the stuff at cost.

Mounted sideways it would look something like this:
- Steel Whip
+ Feedpoint/section insulator/whip support
= Copper pipe with feedline (coax) running through it to feed point
------------------------+===============
Left side connected to center conductor at feedpoint
Right side connected to shield at feedpoint

What I'd like to know is if it is going to have a major effect on my
dimensions/bandwidth/anything else if I use different materials for the
two
sections of the dipole (steel for the whip, copper for the pipe)? And what
kind of effect is having the two different element sizes going to have as
well? (I know increasing element sizes tends to raise overall bandwidth,
but
not sure how only one element will effect the antenna as a whole.)

Also is there going to be any effect from the capacitance between the
shield
braid of my coax and the antenna segment surrounding it? The website I
read
this from didn't mention that, though they did say you may want to coil
the
feedline about 4-6 turns about another quarter wavelength from the end of
the antenna.

Thanks in advance
73
KD4COX, Eric


Eric

I've heard that stainless steel whips disipate a significant amount of
energy ay 50 MHz. If you have several hundred watts, you might want to try
transmitting with the ss whip before finalizing your design. You might be
surprized to find that the whip gets warm quickly.

Jerry

If you put "several hundred" watts -- let's say 300 for an example --,
into a stainless steel whip, and that whip has a trifling 0.5 dB loss,
the whip will be dissipating nearly 37 watts. At 1 dB loss, it'll
dissipate over 77 watts. Either is likely to make the whip too hot to
touch if the power is applied for long -- imagine the heat from a light
bulb of that power rating coming from the antenna. If it only gets good
and warm, you'll know the loss is negligible. If it gets too hot to
touch, the loss could still be negligible. Unless it's glowing, you
won't know for sure.

Larsen antennas has made a very good living, thank you, with their
"Kulrod"(R) plated antennas by capitalizing on the irrational alarm
people have when finding a warm whip antenna.

Roy Lewallen, W7EL

Jerry Martes wrote:


Eric

I've heard that stainless steel whips disipate a significant amount of
energy ay 50 MHz. If you have several hundred watts, you might want to try
transmitting with the ss whip before finalizing your design. You might be
surprized to find that the whip gets warm quickly.

Jerry

Roy

I'd not 'take sides' to condem stainless steel for 50 MHz antennas. The
truth is; I dont actually know what the loss would be for a stainless steel
whip. I'd use ss if there was some compelling reason for using it. But, I
do want to alert anyone who hasnt thought fo it, that there is some loss due
to choosing ss rather than copper or aluminum.
And, I am not implying that a db is all that important. But, when someone
is designing something it is common to want to build it so the maximum
efficiency is acheived.

Jerry



"Roy Lewallen" wrote in message
...
If you put "several hundred" watts -- let's say 300 for an example --,
into a stainless steel whip, and that whip has a trifling 0.5 dB loss,
the whip will be dissipating nearly 37 watts. At 1 dB loss, it'll
dissipate over 77 watts. Either is likely to make the whip too hot to
touch if the power is applied for long -- imagine the heat from a light
bulb of that power rating coming from the antenna. If it only gets good
and warm, you'll know the loss is negligible. If it gets too hot to
touch, the loss could still be negligible. Unless it's glowing, you
won't know for sure.

Larsen antennas has made a very good living, thank you, with their
"Kulrod"(R) plated antennas by capitalizing on the irrational alarm
people have when finding a warm whip antenna.

Roy Lewallen, W7EL

Jerry Martes wrote:


Eric

I've heard that stainless steel whips disipate a significant amount of
energy ay 50 MHz. If you have several hundred watts, you might want to
try
transmitting with the ss whip before finalizing your design. You might
be
surprized to find that the whip gets warm quickly.

Jerry

"Tyas_MT" wrote in message ...
I'm planning on making a 6m vertical dipole, using a tube lower element
(shield side) to run the coax to the center point.
I have an almost perfectly sized stainless steel whip (old CB antenna), and
already have a slightly longer section of copper pipe to use for the bottom
that I can easily cut down. A friend that makes custom plastic stuff says if
he has the proper sized scrap he'll bore and cut a plastic insulator/whip
support for me... if not he'll get the stuff at cost.

Mounted sideways it would look something like this:
- Steel Whip
+ Feedpoint/section insulator/whip support
= Copper pipe with feedline (coax) running through it to feed point
------------------------+===============
Left side connected to center conductor at feedpoint
Right side connected to shield at feedpoint

What I'd like to know is if it is going to have a major effect on my
dimensions/bandwidth/anything else if I use different materials for the two
sections of the dipole (steel for the whip, copper for the pipe)?

No. Not enough to notice.

And what
kind of effect is having the two different element sizes going to have as
well? (I know increasing element sizes tends to raise overall bandwidth, but
not sure how only one element will effect the antenna as a whole.)

Not much...You may have to trim the antenna, but you won't know for
sure until you actually try it.

Also is there going to be any effect from the capacitance between the shield
braid of my coax and the antenna segment surrounding it?


Dunno.. I doubt it...
The website I read
this from didn't mention that, though they did say you may want to coil the
feedline about 4-6 turns about another quarter wavelength from the end of
the antenna.

Yep, that antenna will need feedline decoupling. A 2nd lower 1/4 wave
copper tube, closed at the top and grounded to the shield, and open at
the bottom like a bell, would be even better. I'd at least use a coax
choke. MK

--

"Mark Keith" wrote in message
m...
"Tyas_MT" wrote in message
...

Dunno.. I doubt it...
The website I read
this from didn't mention that, though they did say you may want to coil
the
feedline about 4-6 turns about another quarter wavelength from the end
of
the antenna.

Yep, that antenna will need feedline decoupling. A 2nd lower 1/4 wave
copper tube, closed at the top and grounded to the shield, and open at
the bottom like a bell, would be even better. I'd at least use a coax
choke. MK

I am considering trying to make a feed point balun at the center insulator,
but I won't have much room. I've got it laid out horizontally and it tunes
up pretty good as is, but I have not gotten with the guy to make my little
center insulator.

I'm mounting this above my 6m quad as an omni-vertical... I figure I can
stick it on top of a PVC pipe and it will interfere less with the quad than
a 1/4 ground plane would (and it looks better).

Thanks for the responses... I don't think heating the whip will be a
problem, though loss might... I'm only running 5 watts key down.

I'm really shooting for the occasional cross polarized weak signal
contact... though I think that the difference in gain between the dipole and
the (horizontal polarized) quad will end up meaning that vertical signals
are about the same... but it's worth a shot.

73
KD4COX
Eric